(642d) Characterization of Transport Phenomena During Flash Pyrolysis of Cellulose

Flash pyrolysis is a chemical process which allows conversion of renewable energy sources, e.g. corn stover or switchgrass, into fuels, e.g. cellulosic-ethanol. We have set up a pyrolysis experiment to study basic transport phenomena during the ablative flash pyrolysis of cellulose. In our experimental setup a cellulose rod of 10mm diameter and 300mm length is impinged onto a hot spinning metal surface. The whole setup is enclosed in an atmospheric chamber that contains a mixture of gases at prescribed partial pressures and temperature to favor the pyrolytic reactions of cellulose. In our experimental setup, cellulose ablation is controlled via the angular velocity of the rotating plate and the force of impingement of the cellulose rod. Pyrolysis is controlled via the temperature of the spinning plate and the thermodynamic properties of the combustion gas. The aim of this experiment is to explore the parameter space of cellulose ablation (spinning velocity and impingement force) and pyrolysis kinetics (temperature and combustion composition) in order to find optimum values of pyrolysis vapors. The physical and chemical processes in the impingement zone are observed with an optical pyrometer to analyze the chemical kinetics of cellulose decomposition and with a high-speed camera to capture the ablation dynamics. Furthermore, we analyze flash pyrolysis for various modes of the hot surface motion, e.g. start-up of rotation, steady rotation, cessation of rotation, and oscillatory rotation with small and large amplitudes of oscillation. Our experimental studies are paralleled by theoretical investigations based on the physical modeling of transport phenomena and chemical kinetics. For our theoretical investigation we adopt a standard kinetic model of cellulose flash pyrolysis which considers the formation of activated cellulose with a low degree of polymerization as an intermediate product prior to the formation of char, tar, and gas. Moreover, we discuss whether non-Newtonian properties of cellulose and activated cellulose need to be considered for a more reliable transport modeling of flash pyrolysis and whether our experimental observations can be described in the framework of transport theories for chemically stable polymeric liquids. We propose a set of transport equations for flash pyrolysis and we show how it can be adopted to find a set of process parameters that leads to an optimum production rate of pyrolysis vapors at a minimum energy cost.